How to protect patio furniture from rain

Protecting patio furniture from rain means getting water off it quickly, not keeping water away from it. Clear the drain holes, lift the legs out of standing water, take the cushions in or buy cushions that drain, and use a vented cover over furniture that is already dry. Rain itself damages almost nothing outdoors — trapped water damages everything, and nearly every rain-related failure is a drainage failure wearing a disguise.

The short answer

This reframing is the whole guide. Outdoor furniture is designed to be rained on. It is not designed to hold water, and the difference between those two situations is where all the damage lives:

• A wet aluminum frame is fine. Water inside an aluminum tube with a blocked drain hole is a freeze-expansion problem.
• A wet teak arm is fine. Teak end grain standing in a puddle is wicking moisture into the joint.
• A rained-on acrylic cushion cover is fine. A closed-cell foam cushion that stayed soaked for four days is mildew.
• A wet powder-coated steel leg is fine until the coating chips. Then water is behind the coating, and that is a one-way failure — the rust guide covers it.

What rain actually damages

In rough order of how often it is the actual problem:

• Cushions and slings, via the fill. The fabric is rarely the issue; the interior is. Open-cell quick-dry foam drains and dries in hours. Ordinary closed upholstery foam holds water for days and grows mildew from the inside, which is why the smell appears before any visible mark.
• Steel, at every coating breach. Rain is the delivery mechanism for a failure the chip caused.
• Wood joints and end grain. Not the surfaces. The USDA Forest Products Laboratory's work on wood biodeterioration is a long account of one requirement: decay fungi need sustained moisture, so wood that dries between wettings does not rot regardless of how often it gets wet.
• Fastener holes. Water sits in the annulus around a bolt, and in wood it corrodes plated hardware and stains the timber black around it.
• Glass tabletops and glides, through freeze cycling. Water that collects and then freezes expands, and the expansion finds the weakest joint.

The five things that work

In the order they are worth doing. The first two cost nothing.

• 1. Clear every drain path. Tube frames have drain holes; find them and keep them open. Slatted seats drain through the gaps, so clear the debris that bridges them. Most interior frame corrosion starts with a blocked hole.
• 2. Lift the legs out of standing water. Glides, feet or a paver under each leg. Open tube ends and wood end grain both draw water upward, and a sloping deck or a set of glides removes the mechanism entirely.
• 3. Deal with the cushions. Indoors in a dry box, or buy cushions built for it. Solution-dyed acrylic over open-cell fill is the specification; can cushions get wet goes through the fill types.
• 4. Cover with vents, over dry furniture. In that order. A cover is for keeping water out of places it cannot leave, and it only works on furniture that is dry when you fit it.
• 5. Break the sag. Prop any dip in a cover so rain runs off rather than pooling. Standing water on a cover stretches it permanently and defeats a water-resistant coating in a way falling rain never does.

By material

Three mistakes that make it worse

• Covering wet furniture. The most common and the most damaging. A sealed cover over a damp frame holds the moisture against the metal or wood for weeks instead of hours.
• Sealing instead of draining. Varnishing wood or taping over drain holes attacks the wrong problem. A film finish cracks and traps water underneath; the argument is in oil versus varnish, and the broader case is why you cannot waterproof patio furniture.
• Treating rain as the enemy. Furniture that gets rained on and dries is furniture in normal service. The effort belongs on drainage, cushions and coating breaches, not on keeping water off — which is impossible outdoors anyway.